Pack your bags. But leave the bottled water behind; you might not need it.

Scientists have found a planet orbiting another star — 22 light-years away — and of all the hundreds of so-called exoplanets so far discovered, this one is, lead researcher Guillem Anglada-Escude said, “the new best candidate to support liquid water and, perhaps, life as we know it.”

The planet is labeled GJ 667Cc, found in the constellation Scorpio, and it would seem at first to be a very alien world. It is about five times more massive than Earth. It orbits its host star in only 28 of our days.

But that star is smaller and dimmer than our sun, and most of the light it emits is infrared. Anglada-Escude says it would provide just the right amount of warmth for the planet to be temperate like ours.

“Other proposed candidates [to be watery worlds] would require very special conditions to support liquid water,” Anglada-Escude said in an email to ABC News.

The temperature, he said, is probably right regardless of the planet’s atmosphere or cloud cover: “This one lies within the zone where no further assumptions (or fine tuning) are required.”

Water is actually very common in the universe — but as ice or vapor, not flowing water that scientists say would probably be necessary for life as we know it. Comets, for instance, have been called “dirty snowballs,” and when they get close to the sun they develop gaseous tails. But the temperature range for flowing water — the liquid you would find in the cells of a living organism — is very small. Earth is the only planet we know of with the right temperature and atmospheric pressure.

Some serious cautions are in order, of course, when you’re talking about a planet more than 100 trillion miles away. Scientists cannot see it; all they know is that its gravity pulls on its host star, causing the star to “wobble” slightly in a 28-day cycle. But because they know the star’s mass, composition and brightness, they can do some math and figure out how far away the planet is likely to be.

GJ 667Cc would be a strange place if Earthlings could visit. If it has a solid surface, one would find its gravity crippling. Its sun would loom large in the sky, much larger than Earth’s sun does, but it would be dimmer.

And there would be two other suns in the sky, although they orbit at a distance. One of them would be about as distant as Saturn is from us, the other five times farther away than Pluto is.

The one thing Earthlings would find familiar is the temperature. GJ 667Cc does not get fried the way planets like Mercury and Venus do, and it does not freeze like Jupiter or Pluto. Space researchers like to say it is in the “Goldilocks zone” around its sun, not too hot, not too cold, but just right.

Anglada-Escude and Paul Butler led the research at the Carnegie Institution for Science in Washington. They and a dozen colleagues are publishing their work in Astrophysical Journal Letters.

They report they found the planet by looking through telescope data collected by HARPS, a rival group of planet hunters in Europe. Anglada-Escude said the HARPS group had observed the star three years ago and missed the planet.

“Of course, the HARPS team will not be very happy about this,” Anglada-Escude said. “This might start a new trans-oceanic war.”

“GJ 1214b is like no planet we know of,” said lead author Zachory Berta, from the Harvard Smithsonian Center for Astrophysics.

The planet was discovered in 2009 by ground-based telescopes. It is about 2.7 times the Earth’s diameter, but weighs almost seven times as much. It orbits its red-dwarf star at a distance of just two million km, meaning temperatures on GJ 1214b probably reach above 200C.

In 2010, astronomers released measurements of its atmosphere. These suggested that GJ 1214b’s atmosphere was probably made up of water, but there was another possibility – that the planet was covered in a haze, of the type that envelopes Saturn’s moon Titan.

Mr Berta and his colleagues used the Hubble Space Telescope’s wide-field camera to study the planet as it crossed in front of its star – a transit. During these transits, the star’s light is filtered through the planet’s atmosphere, giving clues to the mixture of gases present.

Hubble’s observations can give clues to gases in the planet’s atmosphere

The researchers said their results are more consistent with a dense atmosphere of water vapour, than one with a haze.

Calculations of the planet’s density also suggest that GJ 1214b has more water than Earth. This means the internal structure of this world would be very different to that of our own.

“The high temperatures and pressures would form exotic materials like ‘hot ice’ or ‘superfluid water’, substances that are completely alien to our everyday experience,” said Dr Berta.

The planet’s short distance from Earth makes it a likely candidate for follow-up observations with the James Webb Space Telescope, which may launch by the end of this decade.

The study has been accepted for publication by the Astrophysical Journal.

In contrast to planets with masses similar to that of Jupiter and higher, the bulk compositions of planets in the so-called super-Earth regime (masses 2–10 times that of the Earth) cannot be uniquely determined from a measurement of mass and radius alone. For these planets, there is a degeneracy between the mass and composition of both the interior and a possible atmosphere in theoretical models. The recently discovered transiting super-Earth exoplanet GJ 1214b is one example of this problem.

Three distinct models for the planet that are consistent with its mass and radius have been suggested. Breaking the degeneracy between these models requires obtaining constraints on the planet’s atmospheric composition. Here we report a ground-based measurement of the transmission spectrum of GJ 1214b between wavelengths of 780 and 1,000 nm.

The lack of features in this spectrum rules out (at 4.9σ confidence) cloud-free atmospheres composed primarily of hydrogen. If the planet’s atmosphere is hydrogen-dominated, then it must contain clouds or hazes that are optically thick at the observed wavelengths at pressures less than 200 mbar. Alternatively, the featureless transmission spectrum is also consistent with the presence of a dense, water vapor atmosphere.